LR mobile offline

Hello

I am using Lightroom mobile on my iPhone 6 with an adobe account. It happens that I don't have an internet connection and still want to work on my photos. However, most of them appear to be black and not visible.

I have been looking for an answer how to work offline on my photos (of course with syncing them when I have internet again), but I haven't found one. One blog (https://lightroomkillertips.com/need-work-offline-lightroom-mobile/) shows a solution but this is either just for iPad or for an older version of LR. I don't have the mentioned button "enabling offline editing".

Does anyone have an answer to my problem? - Thanks in advance!

kindly Pascal